1. Field of the Invention
The present invention relates to ion selective electrodes and more specifically to ion selective electrodes for detecting organic drugs in saliva, sweat, and surface wiper.
2. Description of the Related Art
It is currently estimated that there are over three million hardcore cocaine users and one million hardcore heroin users in the United States. It is also estimated that there are over two million occasional cocaine users and half a million occasional heroin users. Together they consumed 269 metric tons of cocaine and 12.9 metric tons of heroin in 2000 spending $63 billion on illicit drugs. Rhodes, W., Layne, M., Johnston, P., Hozik, L., What America""s Users Spend on Illegal Drugs 1988-1998, Office of National Drug Control Policy, December 2000. One adverse consequence of drug use that appears to be grossly under-publicized is driving under the influence of drugs. Although alcohol contributes to about 39% of the 40,000+ annual fatal traffic accidents and 1.4 million arrests per year, a substantial fraction of those under the influence of alcohol are also under the influence of drugs. Shults, R., Impaired Driving, Dec. 11, 1998, CDC, National Center for Injury Prevention and Control. In a recent study conducted in Nassau County, N.Y. and Houston, Tex., about 36% of 800 drivers arrested for driving while intoxicated also had drug metabolites in their urine. See Hersch, R. K., Crouch, D. J., and Cook, R. F., xe2x80x9cField Test of On-Site Drug Detection Devices,xe2x80x9d DOT HS 809-192, October 2000 and Brookoff, D., Cook, C. S., Williams, C., and Mann, C. S. xe2x80x9cTesting Reckless Drivers for Cocaine and Marijuanaxe2x80x9d, N Engl J Med, 331(8):518-522 (1994) for similar results. Another study showed that 45% of federal prisoners have driven a car while under the influence of drugs (www.ojp.usdoj.gov/bjs). Thus, driving under the influence of drugs (DUID) is a critically important public safety issue.
Campaigns such as Mothers Against Drunk Driving have reduced alcohol-related automobile fatalities over 30% in the past decade. One of the factors that appears to dissuade public interest groups from starting similar campaigns against DUID is the lack of effective tools in the hands of law enforcement officers to rapidly and privately measure drug levels. Once those tools are made widely available, a serious and credible deterrent to occasional drug use would be present. The publicity would both reduce DUID and help make illicit drug use socially unacceptable in the public eye.
During routine traffic stops or DWI (driving while intoxicated) roadblocks, police officers have only a few moments to determine if a drive is under the influence. Besides the usual visual clues, the main tool in current use is the Officer""s sense of smell, which works in a limited way only for alcohol and marijuana. Frequently, individuals who consume drugs also consume alcohol, which provides a synergistic effect. If the alcohol level is below the legal limit, the police officer must make a decision on an arrest. Other drugs of abuse do not provide overt signs of use unless an individual is substantially impaired. Thus, a rapid, fieldable instrument assisting in this decision process would help detect and deter DUID if widely employed.
Urine and blood can be tested to detect drug use. However, the non-private collection method and the long window of detection of drugs in urine (days to weeks) are considered by many to be and invasion of privacy and may not be reflective of the actual safety hazard posed by use of drugs while driving.
Other media, such as saliva and sweat, can also be tested to detect drug use. As shown in FIG. 1, after the first few minutes of use, levels of cocaine in saliva parallel levels in plasma, which are better associated with impairment. If a cocaine cut-off level were set at approximately 50 ng/mL, the window of detection for cocaine in saliva would only be four hours. Because cocaine can only be detected during this short time-frame following cocaine administration, it is easier to demonstrate some impairment in driving performance compared to the several days that urine would test positive. In some operational scenarios, saliva may be too intrusive. Instead, a skin swab may be employed. Although skin swabs measure both passive exposure and use, the absence of drug residues would rule out drug use, except under extraordinary circumstances.
Current technologies to detect drugs in saliva include ion mobility mass spectrometry and immunoassays. Ion mobility mass spectrometry, as exemplified by the Barringer Ion Scan and the Barringer Sabre 2000 (www.barringer.com) or the Ion Track Itemiser and the Ion Track VaporTracer 2 (www.iontrack.com), has the advantage of rapid (1 minute) detection of a wide variety of materials in a semi-quantitative manner. However, it has the disadvantages of high cost ($20 K-$42 K/unit), maintenance, and bulk (shoe-box to suitcase sized). Immunoassays, as exemplified by Securetec Drugwipes (www.securetec.net), have the advantage of simplicity of operation, portability, and low cost ( less than $10/each. U.S. Pat. No. 5,891,649, incorporated herein by reference, discloses the use of immunoassays for detection of drugs in sweat. However, immunoassays are selective for each drug or drug class, and therefore, a separate test must be performed for each substance suspected. Also, they are non-reusable so the reoccurring costs may be prohibitive in high volume applications. In addition, immunoassays only provide a presence or absence indication; quantitative analysis is difficult without instrumentation and then it is linear only over a limited range.
Another technology to detect drugs is ion selective electrodes, which measure ionic species. Ion selective electrodes are well known in the art to measure ionic species such as potassium, lithium, sodium, and calcium. However, developing ion selective electrodes to detect drugs has been limited to detecting drugs in pharmaceutical preparations or to detecting illicit drugs in urine or blood. Information relevant to using ion selective electrodes can be found in the following references: Elnemma, E. M., Hamada, M. A. and Hassan, S. S. M., xe2x80x9cLiquid and Poly (Vinyl Chloride) Matrix Membrane Electrodes for the Selective Determination of Cocaine in Illicit Powders,xe2x80x9d Talants, 39 1329-1335 (1992); Campanella, L., Colapicchioni, C., Tomassetti, M., Bianco, A. and Dezzi, S., xe2x80x9cA New ISFET Device for Cocaine Analysis,xe2x80x9d Sensors and Actuators, 24-25 188-193 (1995); Watanabe, K., Okada, K., Oda, H., Furuno, K., Gomita, Y. and Katsu, T., xe2x80x9cNew Cocaine-Selective Membrane Electrode,xe2x80x9d Analytica Chimica Acta, 316 371-375 (1995); K. Watanabe, K. Okada, and T. Katsu, xe2x80x9cDevelopment of an Amphetamine-Selective Electrode,xe2x80x9d Jpn. J. Toxicol. Environ. Health, 42, 33 (1996); S. S. M. Hassan and E. M. Elnemma, xe2x80x9cAmphetamine Selective Electrodes Based on dibenzo-18-crown-6 and dibenzo-24-crown-8 Liquid Membranes,xe2x80x9d Anal. chem., 61 2189-2192 (1989); K. Watanbe, K. Okada, H. Oda, and T. Katsu, xe2x80x9cDevelopment of a portable cocaine-selective electrode,xe2x80x9d Jpn. J. Toxicol. Environ. Health, 43, 17(1997); L. Campanella, L. Aiello, C. Colapicchioni, and M. Tomassetti, xe2x80x9cLidocane and Benzalkonium Analysis and Titration in Drugs Using New ISFET devices,xe2x80x9d J. Pharm. Biomed. Anal., 18 117-125 (1998); L. Campanella, C. Colapicchioni, M. Tomassetti, and S. Dezzi, xe2x80x9cComparison of Three Analytical Methods for Cocaine Analysis of Illicit Powders,xe2x80x9d J. Pharm. Biomed. Anal., 14 1047-54 (1996); S. S. M. Hassan, E. M. Elnemma, and E. H. El-Naby, xe2x80x9cSolid State Planar Microsensors for Selective Potentiometric Determination of Ethylmorphine,xe2x80x9d Anal. Let., 32 271-285 (1999); E. M. Elnemma and M. A. Hamada, xe2x80x9cPlastic Membrane Electrodes for the Potentiometric Determination of Codeine in Pharmaceutical Preparations,xe2x80x9d Mikrochim Acta, 126 147-151(1997); L. Cunningham and H. Freiser, xe2x80x9cIon-Selective Electrodes for Basic Drugs,xe2x80x9d Anal. Chim. Acta., 139 97-103 (1982); C. R. Martin and H. Freiser, xe2x80x9cIon-Selective Electrodes for the Determination of Phencyclidine,xe2x80x9d Anal. Chem., 52 1772-1774 (1980); G. D. Carmack and H. Freiser, xe2x80x9cAssay of Phenobarbital with an Ion-Selective Electrode,xe2x80x9d Anal. Chem., 49 1577-1579 (1977); Cosofret, V. V. and Buck, R. P., xe2x80x9cRecent Advances in Pharmaceutical Analysis with Potentiometric Membrane Sensors,xe2x80x9d Critical Reviews in Analytical Chemistry, 24, 1-58 (1993); K. Watanbe, K. Okada, H. Oda, And T. Katsu, xe2x80x9cDevelopment of a Portable Cocaine-Selective Electrode,xe2x80x9d Bunseki Kagaku, 46 1019-1023(1997); S. Komorsky-Lovric, I. Galic, and R. Penovski, xe2x80x9cVoltammetric Determination of Cocaine Microparticles,xe2x80x9d Electroanalysis, 11 120-123 (1999); T. Yeow, M. R. Haskard, D. E. Mulcahy, H. I. Seo, and D. H. Kwon, xe2x80x9cA Very Large Integrated pH-ISFET Sensor Array Chip Compatible with Standard CMOS Processes,xe2x80x9d Sensors Actuators B 44 434-440 (1997); U.S. Pat. No. 5,522,978; U.S. Pat. No. 5,914,271; U.S. Pat. No. 5,180,481; U.S. Pat. No. 6,212,418; U.S. Pat. No. 6,087,182; U.S. Pat. No. 6,165,796; U.S. Pat. No. 6,033,914; U.S. Pat. No. 5,531,870; U.S. Pat. No. 5,554,339; U.S. Pat. No. 5,753,519; U.S. Pat. No. 4,713,165; U.S. Pat. No. 4,454,007; and U.S. Pat. No. 4,399,002, all of which are incorporated herein by reference.
The aforementioned problems with the current technologies are overcome by the present invention wherein a hand-held, fieldable drug monitoring system can detect and quantitate cocaine and other carbon-based drugs of abuse in saliva, sweat, and surface wipes by using an ion selective electrode. In a preferred embodiment, an array of ion selective electrodes is used to detect and quantitate a variety of drugs of abuse.
In a preferred embodiment, the ion selective electrode of the present invention has a cast membrane reference electrode and a sensing electrode with a semi-permeable ion selective membrane comprising a hydrophobic polymer, a plasticizer, and an ionophore selective for the organic drug to be tested. In another aspect of the invention a device to detect organic drugs includes at least one ion selective electrode connected to a converter that coverts a voltage reading from the ion selective electrode to a quantitative drug concentration level. Yet another aspect of the invention is a method for detecting organic drugs in saliva, sweat, and surface wipes including the steps of (a) placing the ion selective electrode in a person""s mouth, taking saliva from a person""s mouth and placing the saliva on the ion selective electrode, squeezing a damp surface swab onto the ion selective electrode after wiping a surface, or wiping a surface after wrapping a damp surface swab around the ion selective electrode; (b) ensuring that the ion selective electrode has electrical contact; and (c) converting a voltage reading from the ion selective electrode to a quantitative drug concentration by using a concentration curve. Another aspect of the invention is a method for testing electrical contact in an ion selective electrode including the steps of (a) injecting a voltage pulse into a reference electrode; and (b) determining if there is a corresponding voltage pulse in a sensing electrode. Still another aspect of the invention is a method of making a cast membrane reference electrode including the steps of (a) casting an ionophoric membrane over a hole; (b) filling the interior of the hole with a salt solution; (c) placing a wire into the solution; and (d) sealing the hole.
The present invention results in several advantages. Testing for drugs in saliva, sweat or surface wipes is not invasive to a person""s privacy and does not have a long window of detection, which makes it easier to determine a person""s impairment. Moreover, by using an array of ion selective electrodes to detect drugs, there is rapid detection of a wide variety of drugs in a quantitative manner with low cost, low maintenance, and small size.
Anticipated system applications include roadside sobriety checks by direct testing of saliva, testing for traces of drugs in sweat using a surface wipe or skin swab, and identifying cocaine-containing items using a surface wipe to test for trace drug residues. Another potential application is a reverse drug test. Sometimes, people can present a threat to the public if they don""t take certain drugs, e.g., anti-psychotic and anti-TB drugs. One can envision a case worker visiting an individual under treatment on a random basis, obtaining a saliva sample or skin swab, and testing the specimen in the presence of the test individual. The presence of the proper drug or metabolite above a given level would indicate that the individual was complying with the treatment regime. The absence of the drug or metabolite would indicate that further monitoring or in-patient treatment of the individual would be necessary. The present invention provides a quick, easy, and non-invasive method for determining whether a person has taken necessary drugs.